Add timezone selector

frontend/src/app/components/timezone-selector/timezone-selector.component.ts

@@ -0,0 +1,58 @@
+import { ChangeDetectionStrategy, Component, OnInit } from '@angular/core';
+import { UntypedFormBuilder, UntypedFormGroup } from '@angular/forms';
+import { StorageService } from '@app/services/storage.service';
+import { StateService } from '@app/services/state.service';
+import { timezones } from '@app/app.constants';
+
+
+@Component({
+  selector: 'app-timezone-selector',
+  templateUrl: './timezone-selector.component.html',
+  styleUrls: ['./timezone-selector.component.scss'],
+  changeDetection: ChangeDetectionStrategy.OnPush
+})
+export class TimezoneSelectorComponent implements OnInit {
+  timezoneForm: UntypedFormGroup;
+  timezones = timezones;
+  localTimezoneOffset: string = '';
+  localTimezoneName: string;
+
+  constructor(
+    private formBuilder: UntypedFormBuilder,
+    private stateService: StateService,
+    private storageService: StorageService,
+  ) { }
+
+  ngOnInit() {
+    this.setLocalTimezone();
+    this.timezoneForm = this.formBuilder.group({
+      mode: ['local'],
+    });
+    this.stateService.timezone$.subscribe((mode) => {
+      this.timezoneForm.get('mode')?.setValue(mode);
+    });
+  }
+
+  changeMode() {
+    const newMode = this.timezoneForm.get('mode')?.value;
+    this.storageService.setValue('timezone-preference', newMode);
+    this.stateService.timezone$.next(newMode);
+  }
+
+  setLocalTimezone() {
+    const offset = new Date().getTimezoneOffset();
+    const sign = offset <= 0 ? "+" : "-";
+    const absOffset = Math.abs(offset);
+    const hours = String(Math.floor(absOffset / 60));
+    const minutes = String(absOffset % 60).padStart(2, '0');
+    if (minutes === '00') {
+      this.localTimezoneOffset = `${sign}${hours}`;
+    } else {
+      this.localTimezoneOffset = `${sign}${hours.padStart(2, '0')}:${minutes}`;
+    }
+
+    const timezone = this.timezones.find(tz => tz.offset === this.localTimezoneOffset);
+    this.timezones = this.timezones.filter(tz => tz.offset !== this.localTimezoneOffset && tz.offset !== '+0');
+    this.localTimezoneName = timezone ? timezone.name : '';
+  }
+}